Axle housings of machines used in earth moving, construction, material handling, mining, and the like, are partially filled with oil for lubricating meshing gears and bearings contained in the housings. It is desirable to have a film of oil between meshing gear teeth in order to avoid degradation due to friction and resultant heat that can occur in contact areas of the teeth. Among other things, excessive heat may induce micro-welding between surfaces of the gear teeth which can lead to premature structural failure of the teeth.
Each axle housing typically contains a beveled toothed gear set such as a ring gear and a pinion gear. Those skilled in the art will appreciate that the teeth of the pinion gear mesh with the teeth of the ring gear, and that an output shaft of the transmission of a machine typically powers rotation of the pinion gear. The rotating pinion gear drives the ring gear and transfers power, through the rotating ring gear and differential case, to the wheels of the machine. The gear ratio of the pinion gear to the ring gear typically creates a reduction of the input speed from the transmission and an increase in torque applied to the wheels of the machine.
Generally, the axle housing is filled with enough oil to ensure that gear teeth, including those of the ring and pinion gears, are lubricated. Thus, a larger gear disposed generally vertically within the axle housing (such as the ring gear), which may require a lower fill level of oil in the axle housing, has to rotate through a much deeper oil fill level in order to ensure that other gears (for example, those with smaller diameters and/or those positioned horizontally) as well as the bearings are adequately lubricated by so-called “splash and spray oil”. As such, the oil flow around a large gear, such as the ring gear, is often rendered undesirably turbulent due to depth of oil in which the gear must rotate. The input power required to overcome resistance of the oil to movement of the gear(s) may be referred to as “churning loss” or “parasitic loss.” A churning loss is associated with increased fuel usage as more input power must be applied to compensate for the churning loss.
In addition, the axle housing must be filled with enough oil to lubricate componentry disposed in either end of the axle housing, and particularly within the legs of the axle housing. When, for example, the machine is operating on an incline, the oil in the axle housing tends to flow downhill toward the axle housing leg that is lowest on the incline. This flow pattern may in some instances increase the churning of the oil, or may decrease availability of oil for lubrication of componentry disposed in an opposite leg housing positioned higher on the incline. Neither has a beneficial outcome.
U.S. Pat. No. 6,345,712 to Dewald, et al., issued Feb. 12, 2002 is an example of prior art related to oil associated with differential axle drives. Dewald et al. discloses a lubrication arrangement in which brake lubricating oil is split into bifurcated cooling channels which flow in two different directions, one outwardly toward the wheels, and the other inwardly toward the differential case. Disadvantageously, the approach of Dewald et al. does not lend itself to an integrated oil circulation system within an axle housing. A better design might more effectively return the oil to the central body of an axle housing, to better establish predetermined desirable flows of oil throughout the entire axle housing. Thus, among other things, a unidirectional return oil passageway might improve oil flow from the inclined end of the axle housing when the axle housing is tilted, such as when on a hill by way of example. Because of the nature of hydrostatic forces, an enhanced return flow from the inclined end can actually facilitate an enhanced supply of oil to the inclined end.